Problem: What is $40\%$ of $25$ ?
Having $40\%$ of something means that you get $40$ out of every $100$ We can set up a proportion to find out what number is $40\%$ of $25$ $ \dfrac{{\text{percent}}}{100} = \dfrac{{\text{part}}}{{\text{whole}}}$ Which things do we know, and what are we trying to find? We know the ${\text{percent}}$ is $40$ . Is $25$ the ${\text{part}}$ or the ${\text{whole}}$ The $25$ is the ${\text{whole}}$ . We are trying to find the ${\text{part}}$ that makes up $40\%$ of it: $ \dfrac{{40}}{100} = \dfrac{{\text{part}}}{{25}}$ If we divide the denominator of the fraction on the left by $4$ , it will be the same denominator of the fraction on the right. To keep things equal, let's also divide the numerator on the left by $4$ $ \dfrac{{40} \div 4}{100 \div 4} = \dfrac{{\text{part}}}{{25}}$ $ \dfrac{{10}}{25} = \dfrac{{\text{part}}}{{25}}$ $ {10} = {\text{part}}$ So $10$ is $40\%$ of $25$.